Response of directly seeded high-value timber species to microorganisms, fertiliser and a water retention polymer: implications for reforestation of agricultural lands in Southeast Asia

High-value native timber species are being promoted in reforestation in Southeast Asia. However, slow growth during early establishment, coupled with poor soil fertility, poses challenges for promoting tree planting programs. Field trials were undertaken on agroforestry land in Thailand to examine the efficacy of reforestation treatments. The first trial examined the effect of applying microorganisms and fertiliser on directly seeded Acacia mangium Willdenow, Dalbergia cochinchinensis Pierre and Xylia xylocarpa (Roxburgh) Theobald. After 20 months, a mixed inoculum of arbuscular mycorrhizal and ectomycorrhizal fungi improved survival and basal diameter of D. cochinchinensis by 15 and 43%, respectively. The co-inoculation of arbuscular mycorrhizal fungi and N2-fixing bacteria improved survival by 17%. The second trial investigated the effects of fertiliser and a water retention polymer on directly seeded A. mangium, Afzelia xylocarpa (Kurz) Craib, D. cochinchinensis, Eucalyptus camaldulensis Dehnhardt, Sindora cochinchinensis Baillon and X. xylocarpa. Height was improved by 40% at 20 months. Our findings suggest that reforestation is viable, provided that suitable treatments are used. These principles can be applied for reforestation of nutrient-impoverished soils of continental Southeast Asia.